In coating construction materials, automobile parts and the like, powder coatings have been widely used from the standpoint of operational easiness, environmental pollution and the like. Most of the heretofore proposed powder coatings are based on a resinous composition comprising a base resin having reactive functional group such as polyester resin, epoxy resin and the like, and a hardener, and are cured by baking at a temperature of around 180.degree. C.
However, in order to cut the energy cost involved, it is much preferred to carry out the curing reaction at a lower temperature, and public attentions have been concentrated on studies involving low temperature curable compositions. When glass transition temperature (Tg) of the base resin is an lowered, there is undesired decrease in blocking resistance of the formed powder, and when the number of functional groups in the resin is increased, there is undesired solid-state reaction of the powder during storage, resulting in a coating having a poor appearance. PA0 From the favorable natures of weather resistance, smoothness, gloss and the like, various baking type coating compositions based on the combination of acrylic resin and polyvalent carboxylic acid have been studied. However, in a powder coating area, none of the coating compositions which are satisfiable from the standpoint of low temperature curing, solid-state reaction resistance, blocking resistance, and the like have been found out. PA0 It is, therefore, an object of the invention to provide a resinous composition for powder coating based on an acrylic resin, which is excellent in low temperature curability, blocking resistance and solid-state reaction resistance. PA0 (A) an acrylic resin and (B) a hardener, the acrylic resin being composed of (a) t-butyl methacrylate (TBMA) and/or t-butyl acrylate (TBA), (b) an ethylenically unsaturated monomer having a reactive functional group and (c) other ethylenically unsaturated monomer(s) than the said (a) and (b) which is (are) non-reactive with the reactive functional group possessed by (b), whose reactive functional group content is 0.0010 to 0.0046 mol per gram of resin, glass transition temperature (Tg) is in a range of 30.degree. and 110.degree. C. and number average molecular weight is in a range of 1000 to 20000, and the hardener having in its molecule 2 or more functional groups being reactive with the abovementioned reactive functional group possessed by the acrylic resin.